Telephone system



TELEPHONE SYSTEM Filed Aug 9} 1926 4 Sheets-Sheet 1 v mrenIur'- rank Trench Jan; 14, 1930. F. 'TENCH ,7 07

TELEPHONE SYSTEM I Filed Aug. 9, 1926 4 Sheets-Sheet 2 T fi/Y -InuenIa Frank Tench Jan. 14, 1930. F. TENCH TELEPHONE SYSTEM 7 Filed Aug. 9, 1926 4 Sheets-Sheet 3 IrT.r nZ'n r' I Frank Tench HIT- Jan. 14, 1930; TENQH I I 1,743,407

TELEPHONE SYSTEM Filed Aug. 9 1926 4 Sheets-Sheet 4 AAAAAA Patented Jan. 14, 1930 units stares FRANK TENCI'I, OF LGNDON, ENGLAND, ASSIGNOR, BY IIEESNE ASSIGNDZEIITS, T AS- SOCIATED TELEPHONE & TELEGRAPH COMPANY, OF KANSAS CITY, IIEISSOURI TELEPHOHE SYSTEM Application filed August 9., 1826, Serial No. 128,016, andin Great Britain October 13, 1925.

The present invention relates to telephone systems and is more particularly concerned with systems in which battery for speaking purposes is supplied in the direction O-ftll particularlyapplicable to a system in which the impulses for setting the automatic switches are sent iiia circuit including the two speaking leads in series while the supervisory signals are subsequently transmitted over the speaking leads independently and it may therefore be considered as a development of the system shown in Patent No. 1,672,225, issued June 5, 1928.

in the modification of the arrangement above referred to in such a manner that the source of energy for dialling purposes is located at the outgoing end of the trunk line rather than at the incoming end as hasbeen usual hitherto. This arrangement is found in practice to give improved operating conditions and also enables a number of simplifications to be made in the circuits. The new arrangement retains the feature of the previous invention that the supervisory relays are not connected up or used for any purpose until all the dialling has been done and there is therefore no danger of these relays being operated prematurely and thus causing, for instance, false metering.

According to one feature of the invention, battery and earth are fed forwards from; the

first numerical switch in an exchange over 0 the two speaking leads respectively during dialling through non-supervisory equipment and are fed forwards 0n the completion of dialling through one or more supervisory relays.

According to another feature of the inventiorrthe line relay'of an incoming selector is connected directly across the speaking leads without any battery or earth connections when. the switch isin normal position and The main feature of the invention consists during the-impulsing-period, while after the termination of impulse sending it is connected to one speaking lead only. v

A further feature of the invention isthat in a, telephone system having arrangements for sending selective supervisory signals under the control of a plurality of super.- visory relays adapted to be connected to a single lead, when supervisory signals are to. be transmitted the supervisory relays are connected up automatically in-turn.

The invention will be better understood from the following description of a preferred. embodiment taken in conjunction with the accompanying drawings. It will be under- 7 stood however that the system shown is given by way of example only and that detail modifications could be made by those skilled in the art without exceeding the scope of the invention. Referring now to the drawings, these show by means of the usual circuit diagrams the arrangements of the various switches which may be used in setting up. a connection.

Fig. '1 is a first selector arrangedto feed battery to the calling party and also forward in the direction of the called party.

Fig. 2 is an incoming selector accessible over a-two-conductor trunk and also arranged for battery feeding purposes.

Fig. 3 is an intermediate selector, and Fig. 4 is a connector or final selector. Figs. 5 and 6 show the arrangements for setting up manual to automatic calls with a special operators selector, embodying the principles of the invention.

Fig. 7 shows the apparatus at an-incomin'g operators position, together with a portion of a' cord circuit arranged to work in con junction therewith, and o Fig. 8 shows a desirable modification of the main circuit principles which is applied to an incoming selector, but, it will be understood, could equally well be applied also to' a first selector. l w

A complete connection will. first bet-raced including Figs. 1, 2, 3 and 4, the switches J switch is seized, a circuit is completed for the line relay 5 over conductors 1 and 2 and the subscribers loop. Relay 5 upon operating, at armature 7 completes a circuit for relay 8 and at armature 6 prepares a circuit for reeating impulses to succeeding switches. pon operating, relay 8 at'armature ,9 connects earth to release trunk conductor 3 so as to hold the line switch operated and at point-in the circuit of the supervisory relays V armature 23 prepares a circuit for the ro- 36 and 40. I V

* N 0 further changes take place untilthe subscriber dials the first digit in the wanted number, whereupon a corresponding number of interruptions are produced in the circuit of line relay 5. Upon each release of relay 5,

a circuit is completed from earth, armature, 7 and its back contact, armature 10 and its front contact, winding of relay 13 to battery and parallel thereto by way of armature 33 and its back contact, vertical magnet 35 to battery. The vertical magnet is accordingly operated to raise the switch wipers a corresponding number of steps and relay 13 is energized, and by virtue of its slow-to-release characteristic remains operated throughout the train of impulses. Relay 13 at armature 15 completes a locking circuit for relay 17 over its upper winding, and at armature 16 short-circuits the lower'winding of relay 17, which operation is however without useful effect at this time. .Relay 13 also at armature 14 prepares a circuit for relay 22 which is completed as soon as the switch steps olfnormal, and extends as follows: earth, front contact and armature 9, armature 14 andits front contact, back contact and armature 30, interrupter contacts 26 of the rotary magnet 25, off-normal contacts 27 winding of relay 22 to battery. Relay 22 upon operating, at

taryrmagnetand at armature 24 completes a locking circuit-for itself. At the end of the series of impulses, relay 13 de-energizes, thereupon at armature 14 and its back contact completing a circuit for rotary magnet 25, whereupon the switch wipers are rotated into engagement with the first set of bank 'con-,

tacts in the level to' which they have been raised. Near the end of its stroke rotary magnet 25-opens the interrupter contacts 26, thereby opening the circuit of relay 22 which accordingly de-energizes and at armature 23 opens the circuit of the rotary magnet, which de-energizes also. In case the set of contacts with which the wipers are now in engagement extend to a line which is in use, test wiper 44 will engage an earthed contact, and a circuit will again be completed for stepping relay 22, which therefore energizes and causes the rotary magnet to advance the wipers a further step, whereupon both relay 22 and magnet. 25 are again de-energized. Thisialternate operation of relay 22 and magnet25 continues until test wiper 44 no longer finds earth, whereupon switching relay 28 is no longer short-circuited and energizes in series with relay 22, which is however not now energized owing to the high resistance of relay 28. The operation of relay 28 at armatures 29 and 34 switches the speaking conductors through, at armature 30 connects earth to wiper 44, to busy the seized line, at armature 31opens the initial energizing circuit of relay 17, at armature 32 prepares the circuit of the supervisory relays 36 and 40 and at arma ture 33. opens a point in the circuit for the vertical magnet 35 so as to prevent this magnet from being operated by subsequent trains 'of impulses. Relay 17 does not de-energize at this time in spite of the fact that the circuit over its upper Winding is opened, since a holding circuit is nowcompleted as follows:

battery, armature 19 and its front contact,

front contact and armature 6, front contact and armature29, wiper 45 and the contact with which it is in engagement, conductor 51 extending to the incoming selector, (Fig. 2), winding of line relay 53, normally closed springs controlled by armature 69, ar mature 79 and its back contact, conductor 52, contact engaged by wiper 46 and said wiper, armature 34 and its front contact, armature 21 and its front contact, lower winding of relay 17 to earth- Relay 17 accordingly remalns energized in this circuit and relay 53 also operates, and at armature 55 completes V a circuit for slowrelay 56. The operation of relay 56 prepares the operating circuit of the switch in the usual mannerat armature 58, and at armature57 completes a circuit which extends from earth over back contact and armature 77, upper winding of relay 64 to battery. Relay 64 upon operating performs similar functions to relay 17 in the first selector, namely, at armature 66 cuts out the retard 65, at armatures 67 and 68 prepares locking circuits by way of its upper and lower windings respectively and at armature 69 completes an auxiliary circuit for relay 53 independent of armature 79.

When the subscriber dials the nextseries of impulses, corresponding interruptions are again produced in the circuit of relay 5, which accordingly operates its armatures 6 and 7. The operation of armatures 7 again efleets the energization of relay 13 throughout the train of impulses, and this relay by operating its armature 15 completes a locking circuit for relay 17, so as to maintain this relay energized during the train of impulses While its lower winding is short-circuited at armature 16 so as to improve the impulsing circuit. Relay 5 also at. armature 6 interrupts the circuit of relay 53 and this accordingly .deenergizes correspondingly: and completes a circuit by way of armature 80 and its back contact for vertical magnet 96. Relay 60 is energized throughout the train of impulses in parallel with vertical magnet 96 and at its armature 61 prepares a circuit for stepping relay which becomes effective when the ofi-norrnal contacts close on the first vertical step of the switch. When relay 60 deenergizcs a circuit is completed over armature 61 and its back contact, and armature 72 and its front contact for rotary magnet 71 so that the switch takes one step and the operation of the interrupter contacts then open the locking circuit of relay 70 over armature 7 3. The hunting motion of the'switch then takes place in the same manner as was described in connection with the first selector (Fig. 1) and when test wiper .91 no longer finds earth, switching relay 74 operates in series with stepping relay 70, which latter is however not now operated. Relay 74 at armatures 7 5, 7 6 and 81 connects the wipers 91, 92 and 93 through, at armature 77 opens the initial energizing circuit of relay 64, at armature 78 prepares the circuit for the supervisory relays 82 and 87, at armature 79 opens the original circuit for line relay 53 and prepares a new circuit and at armature 80 opens. a point in r the circuit of vertical magnet 96 so .as to prevent any subsequent operation of this magnet.

It will be assumed that the connection is then extended to the intermediate selector shown in Fig. 3 and consequently when switching through takes place, a circuit may r be traced as follows: battery, armature 66 and its front contact, front contact and armature 54. front contact and armature 75, wiper 92 and the contact with which it is in engagement, lead 101, normally closed springs con trolled by armature 117, winding of line relay 104, lead 102, contact engaged by wiper 93 and said wiper, armature 81 and its front contact, armature 68 and its front contact and the lower winding of relay 64 to earth. Relay 64 is therefore maintained energized in spite of the opening of its initial circuit, and moreover relay 104 in the intermediate selector is operated, and by attracting its armature 105 completes a circuit for release relay 106. The latter energizes in its turn and at armature 107 prepares the switch for operation in the usual manner, at the same time opening a point in the circuit of release magnet 108.

Then the subscriber dials the succeeding digit, interruptions areproducedin thecir-x cult of relay 5 as before, and these areagain. repeatedat contact 6 to relay 53. Armature 54 of this relay is now efiectiveto repeat these: impulses to line relay 104 of the intermediate selector. Relays 13 and 60 operate as before. to short-circuit the lower windings of relays 17 and 64, while at the same time completing locking circuits for the upper windings of these relays. Upon each de-energizationof relay 104, a circuit is completed from earth, back contact and armature 119, armature 105 and its back contact, armature 107' and its front contact, winding of relay 109, winding of Vertical magnet 111 to battery. By the operation of magnet 111 the switch wipersare raised a number of steps corresponding to the digit dialled, and relay 109 is energized and, being slow, remainsenergized throughout the train of impulses. Stepping relay- 112 is energized as usual when the off-normal contacts close upon the first vertical step of the switch, and when rela'y'109 de-energizes, a circuit is completed by way of armatures and 114for rotary magnet 115. The hunting motion of the switch then proceeds in known manner and upon a free trunk being found, relay 116 operates and at its-- armatures 117, 118 and 120 connects its wipers through. Moreover at armature 119 the circuit of relay 106 is opened, and at armature 117 the circuit of relay 104-so-that both these relays de-energize.

Assuming that the system being described is a 5 digit one having a maximum capacity of 100,000 lines, the connection will now be extended-to a connector, for instance that shown in Fig. 4. The circuit for maintaining relay 64 now extends over wiper 122, lead 141, winding of line relay 144, armature and its back contact, armature and its back contact, lead 142, wiper 123, and over the interrupt-ions are repeated by relays 5 and v1 53 as previously described and relay 144 accordingly de-energizes intermittently. Upon the first release of relay 144 a circuit is completed as follows: earth, armature 171 and and its back cont'act,'armature 145 and its back contact, armature 148 and its front contact, off-normal spring 149 and its resting contact, winding of relay 152, winding of Vertical magnet 154 tobattery. As soon as the switch takes its first step however, the

olf-normalsprings shift and the succeeding i impulses, if any, are transmitted by wayof armature 148 and lts front contact over spring 149 andits working contact, armature 153 and its front contact and through the winding of relay 152 as before, this relay having been energized bythe first im ulse. The switch wipers are thus stepped up 111 the usual manner, relay 152 remaining energized throughout this operation. When the series of impulses terminates, relay 152 falls away.

and'consequentlywhen the succeeding and last series of impulses operates relay 144, the

impulsing circuit extends over armature 153 and its back contact, back contact and arma ture162,'armature 173 andits back contact,

winding of rotary magnet 167 to battery and tures-160 and 162 respectively and their back contacts so as to prevent circuits being broken prematurely in case busy relay 159 should be energized owing to the wipers rotating over busy contacts.

It will be assumed in the first instance that the wanted party is idle at this time; consequently when test wiper 175 comes to rest on the contact associated with his line, it will not find earth and the busy relay 159 if previously energized will now de-energize. An instant afterwards, relay 163 de-energizes and acircuit is then completed from earth, frontcontact and armature 147, armature 161 and its back contact, upper winding of the relay 168, back contact and armature. 165,

test wiper 175 and by way of the cut-01f relay and rotary magnet of the subscribers line switch to battery. Relay 168 and the cut off relay energize in series in this circuit but owing to the well-known inter-lockin arrangement between the line and cut-o v relays, the later relays is only able to operate its armatures sufiiciently to clear the line of 'its normal battery and earth connections,

7 but not suflicie'ntly to connect upv the wipers of the line switch. Relay 168 upon operating,

at armatures 169' and 174 connects up its wipers so that ringing current from thelead RM is projected out over the called line, re-

turning by way of armature 156 and its back contact and the upper winding of the ringing trip relay 155 to battery. Relay 168 also at armature 171'connects earth to test wiper.

175 to busy the line, at armature 172 completes a locking circuit for itself by way of its lower winding, at armature 173 opens a a point in the impulsing circuit to prevent any further operation of the rotary-magnet in case the subscriber should dial again, and at armature 170 opens the circuit of line relay 144, at the same time connecting up ringing induction by way of the small condenser 176.

The effect of the opening of the circuit of line relay 144 is to open also the circuit of relay 64 of the incoming selector and this relay accordingly de-energizes, thereby at its across the two speaking leads. I The effect of;

this is to open the circuit of relay 17 in the first selector and this de-energizes with somewhat similar results, the most important of which is the connecting up of the supervisory relays 36 and 40. v 7 r .The circuits remain in this condition until the called party replies, whereupon inconse quence of the direct current bridge across the speaking leads, the ringing trip relay 155 is operated, thereupon at armature 157 completing a locking circuit for itself, and at armatures 156 and 158 disconnecting ringing cur rent and switching the speaking leads through. A circuit is now completed as follows: battery, retard 65, normally closed springs controlledby armature 66, front contact and armature 54, front contact and armature 75, wiper 92, lead 101, front contact and armature 117, wiper 122, lead 141, front con-- tact and armature 156, armature 169 and its" front contact, wiper 177, over the called partys loop, wiper 178, front contact and armature 174, armature 158 and its front con tact, lead 142, wiper 123, armature 120 and its.

front contact, lead 102, wiper 93, armature 81 and its front contact, armature 68 and its back contact, armature 78 and its front contact, lower winding of relay 82, winding'of relay. 87 to earth. Since the call has been made to another automatic subscriber,'the resistance of this circuit is such that both relays 82 and 87 now operate the former at arma ure 83 completing a locking circuitfor itself over its upper winding and at armature 84 short-circuiting the high resistance 86. Relay 87 upon operating, at armature 90 completes a point in an auxiliary circuit for relay 56, another point in which however has previously been opened at armature 85, at armature 89 short-circuits the lower winding of relay 82 so as to give standard talking conditions in every case and at armature 88 connects battery through the retard 97 to conductor 52. The battery connection over lead 52' is extended byway of wiper 46, armature 34 and its front contact, armature21 and its back contact, armature 32 and its front contact, winding of relays 36 and 40 to earth. Since the high resistance 86 has been cut out, both these relays are able to operate, the former locking itself up at armature 37 and at armature 39 connecting earth to the metering conductor 4 so that the successful call is charged against the calling party The operation of relay-40 closes a point 1n an auxiliary circuit for relay 8 at armature 42 and both replace their at armature 11 short circuits the energizing winding of relay 36.

The subscribers may now converse as desired and when they have finished they will receivers. When the receiver reolaced at'the called sub-station, relay 8'? (lo-energizes and opens the'circuit of relay d0, which de-energizes in its turn, but this operation produces no particular eri'ect, though it will be appreciated that relay 40 could be arranged to control a lamp associated with the switch and thus notify an attendant, particularly of the conoition in which the called party had replaced his receiver but the calling party had omitted to do so. ll hen the calling party replaces his receiver, relay 5 de-energizes and at armature 7 opens the circuit of relay 8, which .de-energizes in its turn after a short interval, thereby at armature 9 opening the circuits for relays 28 and 36 and the switching relay of the line switch. Moreover at armature 10 the circuit for the releasemagnet 12 is completed over off-normal springs 11 and this magnet operates to restore the switch to normal. Line relay 5 furthermore at armature 6 opens the circuit for line relay 53 and this de-energizes, thereby opening the circuit for relay 56. V] hen this in its turn falls away, the circuit for release magnet 59 is completed, and the incoming selector is restored to normal. Moreover at armature 57 earth is removed from the release trunk conductor extending to the intermediate selector and connector,

' and this has the effect of bringing down'relays 7 1, 82, 116,155 and 168. Both these switches are then restored to normal by the operation of their respective release magnets 108 and 151, tne circuit for the latter extending from earth, armature 171 and its back contact, armature 145 and its back contact, arntiature 1 18 and its back contact, oil-normal springs 150, winding of magnet 151 to battery. The whole connection has now been released and't-he switches used therein may be employed in setting up another connection.

Consider now the case in'which the called party was lousy when the connector wipers came to rest on his line; in these circumstances wiper 175 will find earth, consequently busy relay 159 will be operated. Thereupon at armature 162 it opens a point in the impulsing circuit to prevent further aeration of rela 163 or rotary magnet 167, t o

at armature 161 prepares a locking circuit for itself and at armature 160 disconnects line relay 1 1 1 and connects up busy tone and intermittent battery through a high resistance by way of the lead BT. An instant later relay 163 deenergizes and a locking circuit is then completed for the busy relay to earth at armature 1 17 and armatures 160 and 162' become etl'e'ctive having'previously been shunted by armatures 164 and 166. Owing tothe opening or the circuit of relay 144, as

relay 1? and as before, this relay connects up relays 36' and 10, but in this case relay only can operate and consequently no metering takes place. As it is assumed that only a subscriber will have access to a selector'of the type shown in Fig. 1, the busy flash battery is in this case without elfect and the subscriber hears busy tone, which is transmitted through the various talking condensers. Accordingly he hangs up his receiver in due course and the whole connection is then released in the manner previously described. c

It may be mentioned at this point that in case any of the selectors used in setting up the connection should be rotated to the eleventh position owing to all trunksin the desired level being busy, the appropriate switching relay would be operated but since the wipers are then disconnected, nomaintaining circuit would be completed for the relay, such as 17 or 64. Consequently this relay deenergizes and efiects the change from inipulsing to supervisory conditions so as to permit of the busy signal being transmitted back. lvloreover the cam springs indicated at 18, 94 and 12 1- in Figs. 1, 2 and 8 respectively are operated and busy tone and intermi ttent battery through a high resistance are" connected to the lower speaking conductor.

Inasmuch however as the first selector, Fig. 1' will not be taken into usefrom an operators position, only busy tone need be connected up at springs 13 since'no prov1s1on need be made for flashing an operators supervisory" lamp.

Consider now the case 1n wlnch a subscr1b er wishes to extend a call to an'operators position, for instance, for information or inquiry. It will be assumed for convenience of description that the switches shown in Figs. 1, 2 and 3 are again employed and that the switch in Fig. 3 when raised to a particular level has access to apparatus at an operators position such as that shown in Fig. l

7: It will be understood of course that in practice access might quite well be obtained to the operators position direct from the bank of the first selector, but with the arrangement above suggested a more complete description 1s possible of the arrangement of the various switches.

When the call-is initiated and impulses are sent out, the operation of the switches shown in Figs. 1, 2 and 3 takes place in the manner above described so that this need not be again considered in detail. When the intermediate selector, Fig. 3, switches through by the operation of relay 116, a circuit is completed as .follows: battery, armature 66 and its front contact, front contact and armature 54, front contact and armature 75, wiper 92, lead 101, front contact and armatuer 117, wiper 122, lead 301, winding of relay 303 to earth. Re-

, lay 303 is operated in this circuit and atits armature 305 completes a circuit for the calling lamp 314 and at its armature 304 connects up ringing induction by way of lead 312 so as to inform the calling party in the same way as on a call to an automatic subscriber that the operator is being signalled. A further effect of the switching-through action of relay 116 is to Open the circuit of relay 64.

' since there is at present no battery connection to lead 302 and this relay, upon de-ener gizing, establishes supervisory conditions in The operation of relay 308 at armature 311 extinguishes the calling lamp 314 and at armature 310 connects the impedance 313 across the jack springs and cuts off the ringing induction. Assuming that the calling party is still on the line so that relay 303 remains operated, a circuit is now completed for the supervisory relays 317 and 320 in series by way of the repeating coils in the cord circuit and impedance 313, and relay 317 by operating its armature 318 extinguishes the supervisory lamp 319. Relay 308 also at armature 309 connects battery to conductor 302 through the retard 306 and the high resistance 307.

The efiect of this is to energize supervisory relay 87, but in view of the inclusion of resistance 307 in the circuit, marginal relay 82 is unable to operate at this time and consequently retard 97 is connected to conductor 52 through the high resistance 86. It will be noticed that since armature90 is now operated, while armature 8 5 is not operated, an auxiliary circuit is completed for release relay 56, this constituting the operators holdup feature. The connection of high resist ance battery to lead 52 in a similar manner produces the energization of relay 40, but not of relay 36, and as the completion of the 'meteringcircuit is dependent only on relay 36, it is clear that no metering can take place in this case. Moreover at armatures 38 and 42 an auxiliary circuit is completed for the release relay 8 similar to that which was I completed for release relay 56 of the incoming selector. V

The subscriber may now make his inquiry or complaint and when he has finished .he will replace his receiver. The effect of this is to de-energize relay 5, which at its armature 7 opens the initial circuit of relay 8, but as previously pointed out this relay is now maintained over the auxiliary circuit. At armature 6 however the circuit for line relay 53 in the incoming selector is opened and this de-energizes, thereby opening the initial cirture 309 the circuit for relay 87 is opened. 7

Consequently relay 56 is now de-energized and the switch is restored in the usual man ner, the removal ofearth at armature 57 from the release trunk conductor 103 initiating the release of the intermediate selector as previously described. In a similar manner the first selector in Fig. 1 is restored to normal upon the release of relay 40 and subsequently relay 8.

The case must now be considered in which a connection is set up froma manual subscriber to an automatic subscriber, for instance by way of the operators position and operators selector shown in Figs. 5 and 6. When the subscriber removes his receiver, hisline relay is energizedinthe usual manner and the calling lamp is lighted; the operator thereupon inserts the plug P into the jack J thus operating the cut-off relay to remove the normal battery and earth connections 7 from the line. The operator then throws her speaking key and .ascertains the calling partys requirements and then inserts the calling plug P into a jack such as J 2 associated with a free'outgoing trunk line. The sleeve relay 204 is thereupon operated in series with the supervisory lamp 210, and relay 204 at armature 205 lights the lamp 206 to indicate that the trunk is busy. The insertion of the plug P has no effect however at present on the operators selector, this arrangement be ing adopted in order to preclude the possibility of the operator sending a false impulse, particularly if she inserts the plug carelessly.

When she throws her diallingkey, however, preparatory to dialling the wanted number, a circuit is completed as followsz battery, closed off-normal springs 202 of the dial, impulse springs 203, working contact and spring 200 of the dialling key K, tip 'ofplug P tip spring of ackJ conductor 251, back contact and armature 281, normally closed springs controlled by armature 269, winding of relay 253 to earth. Relay 253 operates in this circuit: at armature 1 completes a circuit for relay 256 and'at armature 255 prepares a circuit for repeating impulses to sueceeding switches. Upon operating, relay 256 at armature 258 prepares the impulsing circuit and atarmature 257 completesa circuit as'follows earth,front contact and armature 257, back contact and armature 278, upper winding of relay 265 to battery. Belay 265 thereupon at armatures 266 and 267 prepareslocking circuits foritself, at armature 268 connects up battery to-replace that which will be removed-from spring 202 duringdialling, at armature 269 completesa circuit for relay 253 independently of armature 281 and atarmature 270 substitutes a'low-noninductive resistance for the-retard 264. The switch is'now in condition to receive dialled impulses and the operator manipulates the dial in accordance withthe first digit of the wanted number, thereby producing a number of interruptions in the circuit of line relay 253. Each time this relay de-energizes, a circuit is completed over armature 27 9 and its back contact for vertical magnet 283, and

also for the slow relay 260, which is therefore maintained operated throughout the train of impulses. Only armature 261 of relay 260 performs any useful function at this time and this at its front contact prepares a circuit for stepping relay 271, which is completed as soon as the ofl normal contactsclose onthe first step of the switch. Relay 271-in known manner-at armature272 prepares a circuit for rotary magnet273 and at armature 274i completes a locking circuit for itself. When relay 260 de-energizes at theendof the'train of impulses,.the circuit forrotary magnet 273 is completed and the switch wipcrsare rotatedone step. The rotary magnet now interrupts the circuit of stepping relay 271 and the switch subsequentlyhunts to find a free outgoing trunk in a manner which is well understoood. When-such a trunk is found, switching relay 275 operates in series with stepping relay 271' and'at its armaturcs 276, 27 7 and 282 connectsits wipers through. Moreover at armature 278 it opensthe initial energizing circuit of relay 265, atarmature 279 opens a point in the circuit of vertical magnet283 so as to prevent any further-10peration of this magnet, at armature 280 prepares a circuit for connecting up supervisory relay 284, and at armature 281 opens the initial circuit of relay .253. Relay 265 is now held operated over its lower winding, front contact and armature267, front contact and armature 282 line relay of the succeeding switch, which maybe assumed to be an intermediate selector similar to that shownin Fig. 3, armature 27 6 and its front contact, front contact and armature v255,

front contact and armature 270 to battery.

When :succeeding trains of impulses are dialled,-relay 253 isagain operatedintermitset up-or a busy condition has'been encountered, the maintaining circuit for-the lower winding of relay 265 is opened and this-relay de-energises,'therehy connecting up supervisory relay 28 i. Thisrelay is'then' operated in a manner similar to that previously described, when the called party replies, and at itsarinature 285 connects up retard 286 to lead 251. This battery connection is extended over spring 2000f the diallingkey is resting contact ,(since-it has now of course been restored), upper righthand winde ing ofthe repeating coil, winding of relay 207' to earth- Relay 207 is therefore operated and at its armature 209 short-circuits lamp 210, thus giving the operator answeringsupervision. It will be noted that in the operators selector'only one supervisory relay 28% need bEB PIOVlClQd, since the operator herselfeiifects the meteringand is able to determine whether a call is to be charged to the calling part or not. jlVhen both sub scribershave replaced their receivers,lamps 210 and 211 inthe cord circuit will bothlight and the operator will then take down the connection, whereupon all the apparatus will be released in'the usual manner. {It will be noticed that if a busy condition is encountered the intermittent battery connection will energize relay 207 intermittently and thus cause lamp 210 to flash. i 1 p A description will now be given of a modified form of the invention which is shown'in Fig. 8 as applied to'an incoming selector. "It will be understood of course that similar modifications could be made to the other batteryfeeding switches but detailed circuits for these'have not been shown, since the required modifications will be suliiciently obvious to those skilled in the art from a full description of an incoming selector only. It will be assumed in What follows that the switch shown inFig. 8 fits into the switch train'in place of that shown in Fig.2. 'VV'hen' the switch is taken into use from the first selector Fig. 1, a circuit is completed from the pulsing battery over armatures 1'9 and 6 for line relay 353, which circuit extends over the normally closed springs controlled by armature 372 and armature 391 and its back contact, and

as before includes the lower winding of relayl17. Relay 353 therefore operates and at armature 255 completes a circuit forrelay 356 and at armature 354 prepares the impulse repeating circuit. Relay 356 prepares the switch for operation in the usual manner and ers396 and 397 to prevent their exercising any deleterious effect on the impulsing, and moreover at armature 370 prepares the usual circuitfor relay 361 which is energized durmg each train of impulses; When the first digit is sent to the incoming selector, relay 353 de-energizes intermittently in the usual manner and completes circuits forrelay 361 and vertical magnet 394 in parallel. Upon'the terminationof the series of impulses, relay 361' falls back and at armature 362 the usual circuit is completed for initiatin the hunting operation which takes lace owing to the interaction of stepping reay 383 and rotary magnet 386. When a free trunk is found, switching relay 387 is operated and at armatures 388, 389and 393 connects up the switch wipers. At armature 392 the vertical magnet is definitely'cut off, 'at' armature 391 anew circuit is prepared for relay 353 andat armature 390 the initial energizing circuit of relay 366 is opened and a further circuit is prepared for relay 361. Subsequent series of impulses are repeated at armature 354 and relay 361 is energized throughout each train, thereby at armature 363 short-circuiting the lower winding of relay 366, at armature 364 completing a lock-.

ing circuit for this relay by way of itsupper winding and at armature 365 altering the connections of the supervisory relays, though at this time without useful eifect.

When all the impulse sending has taken place, the maintaining circuit over the lower speaking conductor for relay 366 is opened and this'relay de-energizes, thereby at armatures 367 and 373 connecting the speaking leads through and at armature 370 completing a further circuit for relay 361, which extends as follows: earth, front contact and armature 357, armature 390 and its front contact, armature 376 and its backcontact, back contact and armature 370, winding of relay 3 61 to battery. Relay 361 upon operating at this time, connects the lower winding of relay 374 to' the lower speaking lead. The deenergization of relay 366 also at armature 372 opens the circuit of relay 17 in the first elevator so that supervisory conditions are established thereat in the manner previously Jana-m: 1.. ad

described.

The circuits remain in this condition while ringing is taking place, and when the called party removes his receiver, a loop is completed over the two speaking leads in series from battery by way of'retard 360 returning by way of armature 371 and its back contact, front contact and armature 365, winding of relay 374 to ground. It should be mentioned that in this instance relay 374 is arranged to pull up on connections of all classes, while relay-380 is -ma'rginal and only energizes when its circuit does not include a high resistance, that is to say, in the case of calls to automatic subscribers. Hence relay 374 now operates whether the whims been extended to a subscriber or to an operator, and at armature 375 completes a locking circuit for itself over its upper winding, at armature 377 connects battery through retard 395 to lead 352, whence it is extended back to the supervisory relays in the first'selector. Re-v lay 374 moreover at armature 376 opens the circuit of relay 361, which accordingly deenergizes after a short interval. When this occurs the lower winding of relay 374- is cut out and the winding of relay 380 is'substi tuted. In case therefore the connection has been extended to a subscriber, relay 380 will be able to operate and at'armature 381 will short-circuit the high resistance 379 so as to repeat back the supervisory conditions ito the previousswitch. Thus it will be seen that each of the supervisory relays is con nected to the line'alone in turn, and by'this means it is possible to obtain a better operating margin so as to give improved reliabil ity. The release of the switch takes place under the control of the calling party in the usual manner, since unless the operators hold feature represented-by the auxiliary circuit for relay 356' over armatures 378 and 382 is in operation, when relay 353 de-energizes, relay 356' isalso released. ".Thereupon at armature 358 it completes a circuit for the release magnet 359 and at armature 357 removesearth from the release trunk conductor so as to release the succeeding switches under its control.

The modification of the supervisory relay connections just described was devised to overcome a difliculty sometimes experienced under adverse conditions in obtaining complete reliability of operation with a nonoperation of theserelays so that on an opera- .where as on a call to a subscriber which in View of the fact that the two speaking leads are used in series, would tend to involve a greater resistance, only the non-marginal relay is operated and in this case metering takes place. It would probably be desirable 'to render the operation more certain by including a fairly high resistance between the battery feeding retard and the associated speaking lead, this resistance being cut out -on the operation of the non-marginal relay by which time the marginal relay will have been short circuited. Since answering supervision does not take place over this leg on calls to the operator, this resistance is not in cluded in the circuit and'both the supervisory relays will therefore operate. A possible objection to this arrangement is that in case a call is extended over a leaky line, the tendency would be for the current through the supervisory relays to be reduced and in the case of an operator, call when both the supervisory relays should operate, the leak might be suflicient to prevent the marginal relay from picking up, in which case metering would take place when it was not intended.

If this chance 'of trouble were considered serious, it might be overcome by reversing all the battery feed connections so that the supervisory relays were connected to battery instead of to earth. Under these conditions the effect of a leaky line would tend to be to prevent metering when it was really due and the subscriber would not suffer.

The arrangement shown applied in Fig. 8

LU would perhaps be more satisfactory however since there the relays are connected up entirely separately. It will be understood that the two relays could also be connected up in parallel instead of separately as shown in Fig. 8, the essence of the arrangement being 59 ed up temporarily instead of throughout the conversation as in the arrangement of Fig. 8, and in this case it is desirable to arrange that the marginal relay is momentarily connected up each time the subscribers loop is opened so that there is no danger of meter- 1ng not taking place in case the called party removes his receiver clumsily.

It will be understood also that the arrange-= ment shown in Fig. 8 whereby the relay 60 which is up throughout the dialling period disconnects one terminal of the speaking condensers is in no way bound up with the modi= fied supervisory circuits and could be applied without difficulty to the switches shown in Figs. 1, 2 and 6.

What I claim as new and desire to secure by Letters Patent is:

1. In a telephone system, a trunk line terminating in a numerical switch, a train of automatic switches controlled from said first switch to set up a connection, non-supervisory equipment in said first switch for feeding battery and ground forward over the two speaking leads respectively to said automatic switches until the connection is set up, and

means including a retardation coil andtwo supervisory relays in said first switch for feeding battery and ground forward over the two speaking leads respectively after the connection has been set up.

2. In a telephone system, a plurality of automatic switches, meansfor transmitting a plurality of series of impulses over the two speaking leads in series to operate said switches to set up a connection, a plurality of supervisoryrelays, and means for connecting said relays automatically in turn to only one of the speaking leads in the connection set up to control the sending of supervisory signals when the setting operation has been completed.

3. In a telephone system, a trunk line terminating in a numerical switch, a train of automatic switches controlled from said first switch to set up a connection, non-supervisory equipment in said first switch for feeding battery and ground forward over the two speaking leads respectively to said automatic switches until the connection is set up, means including one or more supervisory relays in said first switch for feeding battery and ground forward over the two speaking leads respectively after the connection has been set up, a slow-acting changeover relay included in said non-supervisory equipment, and means including said relay for changing the battery feed from said non-supervisory connection to the supervisory connection after the setting operation has been completed.

4. In a telephone system, a trunk line terminating in a numerical switch, a train of automatic switches controlled from said first switch to set up a connection, non-supervisory equipment in said first switch for feeding battery and ground forward over the two speaking leads respectively to said automatic switches until the connection is set up,means including one or more supervisory relays in said first switch for feeding battery and ground forward over the two speaking leads respectively after the connection has been set up, a slow-acting change-over relay included in said non-supervisory equipment, means including said relay for changing the battery feed from said non-supervisory connection to the supervisory connection after the setting operation has been completed, and means for maintaining said change-over relay energized during the setting up of the connection in a circuit including the two I ergy at the outgoing end.

V supervisory speaking leads in series and a sourceof en- 5. In a telephone system, a trunk line terminating in a numerical switch, a train of automat c switches controlled from said first switch to set up a connection, nonssupervis ory equipment in said first switch for feeding batter and ground forward over the two speaking eads respectively to said automatic switches until the connection is set up, means including one or more supervisory relays in said first switch for feeding battery and ground forward over the two speakingleads respectively after the connection has been set up, a change-over relay included in said nonequipment, means including said relay for c anging the battery feed from said non-supervisory connection to the supervisory connect-ion after the setting operation has been completed, means for short circuiting said change-over relay during the sending of impulses to improve impulsing, a series relay, and means controlled by said series relay for maintaining said change-over relay energized while it is short circuited.

6. In a telephone system, a trunk line terminating in an incoming selector, a line rela-yv in said selector connected across the speaking leads of said trunk line without battery or ground connections when said selector is in normal position and during the impulsing period, and means operative after the termination of impulse sending for connecting said line relay to only one of the speaking leads of said trunk line.

7. In a telephone system, a plurality of automatic switches, means for transmitting a plurality of series of impulses over the two speaking leads in series to operate said switches to set up a connection, a plurality of supervisory relays, and means including a timing device for connecting said relays automatically in turn to only one of the speaking leads in the connection set up to control the sending of supervisory signals when the setting operation has been completed.

8. In a telephone system, a trunk line terminating in an incoming selector repeater, automatic switches, a line relay in said repeater bridged across the two conductors of said trunk line, means for feeding battery and ound forward over the two conductors of said trunk line in series to said repeater to energize said relay, means for interrupting one conductor of said trunk line, to inter- A mittently operate said line relay, means con- 7 one trunk conductor.

" 9. In a telephone system, a trunk line terminating in an incoming selector, a linerelay in said selector connected across the speaking leads of said trunk line without battery or ground connections when saidv selector is in normal position and during the impulsing period, a train of automatic switches, means controlled by said line relay responsive to impulses received for successively controlling said switches in said train to complete a connection, and means responsive to the last switch in said train completing its operation for conrecting said line relay to only one of the speaking leads of said trunk.

11. In a telephone system, a trunk line terminating in an incoming selector, a line relay in said selector normally connected across the talking conductors of said trunk line without battery or ground connections, means operative responsive to the seizure'of said switch for energizing and maintaining said relay bridged across said talking conductors, and means responsive to the termination of a complete series of impulses for rendering said first means inoperative whereby said relay the talking conductors of said trunk line without battery or ground connections, means operative responsive to the seizure of said switch for energizing and maintaining said relay bridged across said talking conductors, means operative responsive to the termination of a complete series of impulses for opening said bridge and for completing a holding circuit for said relay including only one of said conductors, and means in said selector for thereafter transmitting supervisory signals over the other of said conductors.

In testimony whereof I have signed my name at London, England, this 29th day of June 1926.

FRANK 'TENCH. 

